Fiberglass hood mods... crazy?

Bill Dedman said

DANO said: "The engine bay is a low pressure zone,

I am at a loss to understand what forces are at work to create "low pressure zone" underhood, when the radiator is a big, gaping hole in the front of the engine compartment and the inertia of the air in front of a vehicle travelling at high speed literally shoves that air through the radiator and into the engine compartment. Why doesn't that create a high pressure area in the engine compartment? Where does all that air go? The only escape route for it, on a flat-hood car, is to exit underneath the car, which is another high pressure area. That's why cars "lift" at speed, unless they're fitted with some sort of ground-effects (chin spoiler?) I can't see that under-car areodynamic environment "sucking" air from the engine compartment faster than the radiator opening and 100+ MPH of pressure is filling it up.

What am I missing here?

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Path of least resistance. It is easier for air to go around the nose of your car than to go through the grill, header panel, radiator, etc. What air does enter hits the back of your firewall and travels down and under the car. I think this is why most firewalls have a tapered or somewhat rounded firewall to floor board transition. In more modern cars a lot has been done to increase this flow, getting it where is need to be and getting it back out. Your radiator should be the only air access to the engine bay from the nose of the car. At low speed air can pass more easily, but at high speeds it doesn't. I think if you took a fan and put it next to a window screen, place it on low, the air will pass and the screen will not deflect, put the fan on high and the screen will begin to deflect and blow around the screen as not all the air can pass, the nose of a car acts the same way.

Under the car can be a different story, as you know it is not flat, plus stuff hangs down and causes turbulent air friction. Chin spoilers create a wake of sorts to limit air from entering the front and sides, to a point.